The state on Tuesday postponed indefinitely the execution of a condemned killer amid a court battle over the state's method of lethal injection and the role doctors may play in the death chamber.

State officials notified the federal courts they would be unable to comply with a judge's order to have a medical profesional administer a lethal dose of barbiturate to Michael Morales in the execution chamber, a court spokeswoman told The Associated Press.

It was unclear when the execution would be carried out. Prison officials were not immediately available for comment.

Morales, 46, was supposed to die by lethal injection at 12:01 a.m. But the execution was put off until at least Tuesday night after the anesthesiologists objected that they might have to advise the executioner if the inmate woke up or appeared to suffer pain.

"Any such intervention would clearly be medically unethical," the doctors, whose identities were not released, said in a statement. "As a result, we have withdrawn from participation in this current process."

The doctors had been brought in by a federal judge after Morales' attorneys argued that the three-part lethal injection process violates the Eighth Amendment prohibition against cruel and unusual punishment. The attorneys said a prisoner could feel excruciating pain from the last two chemicals if he were not fully sedated.

U.S. District Judge Jeremy Fogel gave prison officials a choice last week: bring in doctors to ensure Morales was properly anesthetized, or skip the usual paralyzing and heart-stopping drugs and execute him with an overdose of a sedative.

Prison officials had planned to press forward with the execution Tuesday night using the second option. The judge approved that decision, but said the sedative must be administered in the execution chamber by a person who is licensed by the state to inject medications intravenously. That group would include doctors, nurses and other medical technicians.

Morales' lawyers planned to appeal to the 9th U.S. Circuit Court of Appeals, but the state notified the court late Tuesday afternoon that it did not intend to go forward with the execution.

The judge's ruling renewed an ethical debate that has persisted for many years about the proper role of doctors in executions and the suitability of the lethal injection method used in California and 35 other states.

The American Medical Association, the American Society of Anesthesiologists and the California Medical Association all opposed the anesthesiologists' participation as unethical and unprofessional.

The anesthesiologists ultimately withdrew after the judge wrote that they might have to demand that the executioner administer more sedatives through a separate intravenous line to make sure the prisoner is unconscious.

The anesthesiologists would have joined another doctor who is on duty at all California executions to declare the prisoner dead and ensure proper medical procedures are followed. The doctor does not insert any of the intravenous lines and is not in the room during the execution itself; typically the doctor watches the inmate's vital signs on electronic monitors outside the death chamber.

Deborah Denno, a Fordham University law professor and expert on lethal injection, said Fogel's order seemed "like a desperate measure."

"These are not circumstances by which somebody ought to be executed," she said. "It's never been done before like this."

The U.S. Supreme Court has never directly addressed the constitutionality of lethal injection or whether it causes inmates excessive pain.

Morales was condemned in 1983 for killing 17-year-old Terri Winchell, who was attacked with a hammer, stabbed and left to die half-naked in a vineyard.

Morales had plotted the killing with a gay cousin who was jealous of Winchell's relationship with another man. The cousin was sentenced to life in prison without parole.